Question
Discuss structure of the carbonyl group.
✓
Answer
→ The carbonyl carbon atom is sp2-hybridised and forms three sigma (σ) bonds.
→ The fourth valence electron of carbon remains in its p-orbital and forms a π-bond with oxygen by overlap with p-orbital of an oxygen.
→ In addition, the oxygen atom also has two non bonding electron pairs. Thus, the carbonyl carbon and the three atoms attached to it lie in the same plane and the π-electron cloud is above and below this plane.
→ The bond angles are approximately 120° as expected of a trigonal coplanar structure (Fig.).
→ The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. Hence, the carbonyl carbon is an electrophilic (Lewis acid), and carbonyl oxygen, a nucleophilic (Lewis base) centre. Carbonyl compounds have significant dipole moments and are polar than ethers. The high polarity of the carbonyl group is explained on the basis of resonance involving neutral (A) and a dipolar (B) structures as shown.
→ The fourth valence electron of carbon remains in its p-orbital and forms a π-bond with oxygen by overlap with p-orbital of an oxygen.
→ In addition, the oxygen atom also has two non bonding electron pairs. Thus, the carbonyl carbon and the three atoms attached to it lie in the same plane and the π-electron cloud is above and below this plane.
→ The bond angles are approximately 120° as expected of a trigonal coplanar structure (Fig.).
→ The carbon-oxygen double bond is polarised due to higher electronegativity of oxygen relative to carbon. Hence, the carbonyl carbon is an electrophilic (Lewis acid), and carbonyl oxygen, a nucleophilic (Lewis base) centre. Carbonyl compounds have significant dipole moments and are polar than ethers. The high polarity of the carbonyl group is explained on the basis of resonance involving neutral (A) and a dipolar (B) structures as shown.
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